Vanadium oxide VxOy exists in many forms and phases (e.g., x is from 1 to 5, y is from 1 to 13). For instance, vanadium (V) has five common valence states, and oxygen (O) content can vary based on this valence state. In addition, different forms or phases can exist at the same reaction conditions, where metastable and/or insulative forms can co-exist with a desired tetragonal, crystalline form. Thus, control of these reactions conditions is critical to obtain the desired vanadium oxide form with the desired stoichiometry.
In particular, the crystalline form of VO2 has interesting transition characteristics. This form is a metal-insulator-transition (MIT) material, meaning that crystalline VO2 undergoes a temperature-dependent crystal structural change, which in turn results in an electronic structure change.
This transition provides two key changes in material characteristics. First, the resistivity of the material depends on the ambient temperature T. For VO2, the material is an insulator at T below the transition temperature Tc (T<Tc) but a metallic conductor at T>Tc. Second, some optical properties (e.g., absorption and refractive indices) of the material also depend on T. For instance, the VO2 material absorbs infrared (IR) radiation for T<Tc but reflects IR for T>Tc.
These temperature-dependent characteristics can be useful for any number of applications, including temperature-dependent switches, electronics, oscillators, memristors, films, coatings, and sensors. For these applications, large quantities of high purity and quality vanadium oxide are desired. As yet, synthesizing these materials in such a manner is challenging and generally requires complicated reaction protocols. Accordingly, simplified methods and protocols to control vanadium oxide formation are needed.